A liquid crystal display device including a transmissive liquid crystal display panel includes a backlight unit that is disposed behind the liquid crystal display panel to project light thereonto. Aside (edge) backlight unit is known as this kind of backlight unit, which includes a light guide plate having a plate shape that is made from a transparent material such as an acrylate resin, and a light source that includes a cold cathode tube (fluorescent lamp) or an LED (Light-Emitting Diode) that is disposed along one side or more than one side of the light guide plate. The side backlight unit described above has an advantage such that a thin profile thereof can be easily achieved compared with a direct backlight unit including a light source disposed behind a liquid crystal display panel.
In particular, a liquid crystal display device that includes an LED as a light source of a side backlight unit has the advantages of long life and high luminous efficiency, and thus has been receiving attention. FIG. 10 is an exploded perspective view showing a schematic configuration of a liquid crystal display device including this kind of side backlight unit including LEDs. FIG. 11 is a cross-sectional view showing a relevant portion of the same.
As shown in FIG. 10, a liquid crystal display device 100 includes a bezel 102, a liquid crystal display panel 103, and a backlight unit 104.
The bezel 102 has a square frame shape with an opening so as to cover edge portions of the liquid crystal display panel 103, and is arranged to, together with a backlight chassis 114, ensure strength of the entire liquid crystal display device 100. The liquid crystal display panel 103 includes two glasses that are bonded together, and liquid crystals are filled in a space between the glasses. The liquid crystal display panel 103 is capable of displaying an image on its front face.
The backlight unit 104 includes the backlight chassis 114 having the shape of a box of low height. The chassis 114 houses optical sheets 107 to 109, a light guide plate 111, a reflection sheet 113, and two LED substrates 120.
As shown in FIG. 11, the light guide plate 111 includes a light incidence surface 111a arrange to obtain light from the LEDs 121 of the LED substrates 120, and a light emitting surface 111b arrange to emit the light upward (in a direction to project the light), which is obtained from the light incidence surface 111a. The light incidence surface 111a is defined by a given side surface of the light guide plate 111, and the light emitting surface 111b is defined by a front surface of the light guide plate 111.
The reflection sheet 113 is disposed so as to cover a back surface 111c of the light guide plate 111, which is the opposite surface to the light emitting surface 111b. The optical sheets 107 to 109 define optical sheets such as a diffusion sheet and a lens sheet, and are disposed above the light emitting surface 111b of the light guide plate 111.
The optical sheets 107 to 109, the light guide plate 111 and the reflection sheet 113 are stacked and fixed onto a bottom plate 114a of the backlight chassis 114 by a frame 105.
In addition, the LEDs 121 provided to the LED substrates 120 are disposed close to the light incidence surface 111a of the light guide plate 111. Further, light emitting surfaces 121d of the LEDs 121 are disposed along the light incidence surface 111a of the light guide plate 111, having a given space therebetween so as to be opposed to the light incidence surface 111a. In this case, the two LED substrates 120 are fixed so as to be disposed laterally while standing on a fixing plate 115 having the shape of the letter “L” that is provided so as to stand on the bottom plate 114a in the vicinity of a side wall 114b of the backlight chassis 114.
Each LED substrate 120 includes wiring patterns 131, 132 and 133 that are formed on a radiating plate made from metal such as aluminum while sandwiching therebetween an insulating layer, and the LEDs 121 are disposed on each LED substrate 120 so as to be connected to the wiring patterns 131, 132 and 133, as shown in FIG. 12.
In this case, four LEDs 121 are disposed linearly along a longitudinal direction of each LED substrate 120, and connected to one another in series by the connecting patterns 131 and 132.
The first LED 121 from the right end of each LED substrate 120 is connected to one end of the light source pattern 131. The other end of the light source pattern 131 is connected to a light-source-side terminal (positive terminal) 141 of a substrate connector 140 disposed at the right end of each LED substrate 120.
The first LED 121 from the left end of each LED substrate 120 (the fourth LED 121 from the right end) is connected to one end of the ground pattern 133. The other end of the ground pattern 133, which extends from the left end of each LED substrate 120 so as to be folded back in a rightward direction along the longitudinal direction of each LED substrate 120, is connected to a ground-side terminal (negative terminal) 142 of the substrate connector 140.
In this case, the substrate connectors 140 have a configuration of being connected to a power substrate 118 included in the liquid crystal display device 100 via cable connectors 150 and cables 161 and 162 arranged to be fitted and connected to the substrate connectors 140.
In the LED substrates 120 having the configuration described above, the substrate connectors 140 connected to the LEDs 121 are disposed at either different ones of right and left ends of the LED substrates 120. Thus, when the two LED substrates 120 are disposed laterally as shown in FIG. 13, the substrate connectors 140 of the LED substrates 120 are disposed so as not to be adjacent to each other by disposing the LED substrate 120 to the left, on which the substrate connector 140 is disposed at the left end, and disposing the LED substrate 120 to the right, on which the substrate connector 140 is disposed at the right end. This configuration allows a distance P2 between the first LED 121 from the right end of the left LED substrate 120 and the first LED 121 from the left end of the right LED substrate 120 to be equal to a distance P1 between the adjacent LEDs 121 (P2=P1). Thus, the light from the LEDs 121 of the two LED substrates 120 can uniformly enter the light incidence surface 111a of the light guide plate 111.
In this case, if the LED substrate 120 is disposed to the left, on which the substrate connector 140 is disposed at the right end, and the LED substrate 120 is disposed to the right, on which the substrate connector 140 is disposed at the right end as shown in FIG. 14A, a problem arises such that the cable connector 150 and the cables 161 and 162 arranged to be fitted and connected to the substrate connector 140 of the left LED substrate 120 interfere with a left end portion or the LED 121 of the right LED substrate 120.
In addition, the ends of the LED substrates 120 on the sides of the substrate connectors 140 are longer by a size of the substrate connectors 140, so that a distance P3 between the first LED 121 from the right end of the left LED substrate 120 and the first LED 121 from the left end of the right LED substrate 120 is longer than the distance P1 between the adjacent LEDs 121 (P3>P1) as shown in FIG. 14A. Thus, the light from the LEDs 121 of the two LED substrates 120 cannot uniformly enter the light incidence surface 111a of the light guide plate 111, which causes a problem such that luminance on the light emitting surface 111b of the light guide plate 111 becomes nonuniform.
In order to prevent these problems, when the two LED substrates 120 are disposed laterally as shown in FIG. 13, the LED substrates 120 of two different kinds are prepared, on which the substrate connectors 140 are disposed at different ends of right and left ends, and disposed so as to have the configuration that the LED substrate 120 is disposed to the left, on which the substrate connector 140 is disposed at the left end, and the LED substrate 120 is disposed to the right, on which the substrate connector 140 is disposed at the right end. A prior art literature of the present invention relates to is provided below.